Electron beam forming for energy analyzers

Abstract

The invention relates to an electron imaging apparatus (23) configured to be connected to an energy analyzer apparatus. The electron imaging apparatus comprises a receiving aperture (22), a control unit, and a field generating unit (65). The receiving aperture is configured for receiving electrons from a focal volume (200) which form an electron beam (25). The control unit is configured for providing a control signal to the field generating unit based on a desired height of the electron beam in an energy dispersive direction (y) of the energy analyzer apparatus at a proximal end (90) of the electron imaging apparatus and a desired angular distribution (α p ) in the energy dispersive direction at the proximal end. The field generating unit is configured for generating at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting a force on the electrons of the electron beam in the energy dispersive direction such that a height of the electron beam in the energy dispersive direction at the proximal end corresponds to the desired height in the energy dispersive direction at the proximal end and an angular distribution in the energy dispersive direction at the proximal end corresponds to the desired angular distribution in the energy dispersive direction at the proximal end.

Description

[0001] APPLICANT:

[0002] SPECS Surface Nano Analysis GmbH

[0003] Voltastrasse 5

[0004] 13355 Berlin

[0005] Germany

[0006] Electron beam forming for energy analyzers

[0007] FIELD OF THE INVENTION

[0008] The present invention relates to an electron imaging apparatus for an energy analyzer, an electron spectrometer apparatus with the electron imaging apparatus, a material analysis system with the electron spectrometer apparatus, a method for operating the electron imaging apparatus, and a corresponding computer program product. In particular, the present invention relates to an electron imaging apparatus, e.g., in form of a beam forming lens for forming an electron beam to a desired shape and with a desired angular distribution at an entrance slit of an energy analyzer, such as a hemispherical energy analyzer of a photoelectron spectrometer.

[0009] BACKGROUND OF THE INVENTION US 4,554,457 A discloses a magnetic rotator lens for rotating the momenta of particles transverse to the direction of a beam. The rotator lens includes a solenoid axially aligned with the beam and employs a magnetic permeable flux return structure surrounding the solenoid. The flux return structure includes beam entrance and exit plates with magnetic permeable and charged particle permeable portions forming the beam entrance and exit ports of the magnetic lens. In a typical example, the beam entrance magnetic permeable and beam permeable portion of the pole piece structure is formed by a grid of magnetic permeable members. The magnetic permeable and beam permeable portions of the pole structures terminate the axial magnetic field without introducing any substantial transverse components to the magnetic field which would otherwise produce undesired rotation of the beam shape. The magnetic rotator lens is employed to advantage in a surface analyzer for focusing a ribbon shaped beam of photoelectrons through the entrance slit of a spherical electrostatic analyzer.

[0010] The publication ’’Argus CUNext Generation Hemispherical Analysed, dated 14.04.2021 by Omicron NanoTechnology GmbH discloses an hemispherical energy analyzer with a compression lens. The compression lens technology allows to transform a divergent electron beam originating from an extended round analysis area into a flat beam that passes the entrance slit of the hemispherical energy analyzer. This is achieved by compressing electrons in the non-dispersiveplane.

[0011] US 6,104,029 A discloses a spectrometer and method of spectroscopy for surface analysis. The spectrometer comprises an energy analyzer for analyzing the energies of charged particles liberated from a sample, a lens arranged to project a diffraction image of the analysis area at the image plane of the lens and a detector for detecting the charged particles. The analyzer and lens are arranged to generate an image at the detector in which the charged particles are distributed along a first direction according to their emission angles and are distributed along another direction according to their energies. The detector is arranged to detect the distribution of charged particles in the image along the first direction to provide angle resolved energy spectra.

[0012] SUMMARY OF THE INVENTION

[0013] It can be seen as an object of the present invention to provide an electron imaging apparatus configured to be connected to an energy analyzer apparatus, an electron spectrometer apparatus with the electron imaging apparatus, a material analysis system with the electron spectrometer apparatus, a method for operating the electron imaging apparatus, a computer program product, and a computer readable medium which allow improved beam forming and angular distribution manipulation of an electron beam to be received by an energy analyzer apparatus.

[0014] In a first aspect of the present invention an electron imaging apparatus configured for transferring an electron beam along an electron-optical axis extending along a center axis of the electron imaging apparatus from its distal end to its proximal end is presented. The proximal end is configured to be connected to an energy analyzer apparatus. The electron imaging apparatus comprises a receiving aperture, a field generating unit, and a control unit. The receiving aperture is arranged at the distal end and configured for receiving electrons from a focal volume emitting electrons from multiple start positions with multiple start angles relative to the electron-optical axis. The electrons received by the receiving aperture form an electron beam with a start cross section at a surface of the focal volume and a start angular distribution based on the start angles of the electrons received by the receiving aperture. The field generating unit is configured for generating at least one electrostatic, magnetic, or electrostatic and magnetic field. The control unit is configured for providing at least one control signal to the field generating unit based on a desired height of the electron beam in an energy dispersive direction of the energy analyzer apparatus at the proximal end and a desired angular distribution in the energy dispersive direction at the proximal end. The field generating unit is configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting a force on the electrons of the electron beam in the energy dispersive direction such that a height of the electronbeam in the energy dispersive direction at the proximal end corresponds to the desired height in the energy dispersive direction at the proximal end and an angular distribution in the energy dispersive direction at the proximal end corresponds to the desired angular distribution in the energy dispersive direction at the proximal end.

[0015] Since the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting a force on the electrons of the electron beam in the energy dispersive direction such that a height of the electron beam in the energy dispersive direction at the proximal end corresponds to the desired height in the energy dispersive direction at the proximal end and an angular distribution in the energy dispersive direction at the proximal end corresponds to the desired angular distribution in the energy dispersive direction at the proximal end the electron beam can be formed while simultaneously manipulating the angular distribution. By adapting the height in the energy dispersive direction and the angular distribution in the energy dispersive direction of the electron beam, a desired energy resolution and intensity or count rate can be achieved at the energy analyzer apparatus when the electron imaging apparatus is used for transferring the electron beam from the focal volume to the energy analyzer apparatus. Furthermore, the electron imaging apparatus allows to select the desired height in the energy dispersive direction and the desired angular distribution in the energy dispersive direction independently from each other within certain limits. This allows increasing a measured intensity or a count rate of electrons at a detector connected to the energy analyzer apparatus while maintaining energy resolution, angular resolution or lateral resolution. For example, the count rate of the detector may be doubled while maintaining energy resolution and angular resolution or lateral resolution.

[0016] The electron imaging apparatus is particularly beneficial in case of large acceptance cross section and large acceptance angular distribution at the distal end as the energy resolution may be significantly lowered in case that the beam is not formed in the electron imaging apparatus before entering the energy analyzer apparatus.

[0017] The inventors found that using a single quadrupole for forming the electron beam allows compression of an electron beam in the energy dispersive direction and projecting an image in one direction and an angular image in a direction perpendicular to the direction in which the image is projected. However, using a single quadrupole is not sufficient to adapt both the height and angular distribution to a desired height in the energy dispersive direction and desired angular distribution in the energy dispersive direction as the angular distribution in the energy dispersive direction and the non-energy dispersive direction perpendicular to the energy dispersive direction are fixed by electron optical theory. The angles of the electron trajectories at the proximal end are approximately proportional to the inverse of a compression factor in the energy dispersive direction.

[0018] The electron imaging apparatus may, for example, be an electron lens of an electronspectrometer apparatus. The electron lens may be connected to an energy analyzer apparatus, e.g., a hemispherical energy analyzer. The energy analyzer apparatus may be connected to a detector, e.g., a position sensitive detector, for detecting the electrons of the electron beam. This allows performing photoelectron spectroscopy. The electron imaging apparatus may be used in an X-ray photoelectron spectroscopy (XPS) system, e.g., a near ambient pressure (NAP) XPS system.

[0019] The focal volume may be inside of a solid or a fluid, such as a liquid or a gas, or a mixture thereof. This allows studying various materials in various physical states. For example, the focal volume may be inside of a sample in form of a solid device or layered structure. In this case, the surface of the focal volume may be, for example, a surface of the sample.

[0020] The number of different start positions of the electrons depends on the focal volume from which the electrons are emitted. The focal volume depends on a spot size, e.g., between 1 pm and 400 pm, preferably between 10 pm and 100 pm, of an X-ray monochromator which focuses monochromatic X-rays in the focal volume.

[0021] The height of the electron beam in the energy dispersive direction corresponds to a distance between the electron trajectories farthest away to each other in the energy dispersive direction. A width of the electron beam in a direction perpendicular to the energy dispersive direction, e.g., a non-energy dispersive direction, corresponds to a distance between the electron trajectories farthest away to each other in the direction perpendicular to the energy dispersive direction. The formed electron beam may be considered to be a sheet beam or elliptically shaped beam with two elliptical axes of which one corresponds to the height of the beam and the other to the width of the beam. The electron beam may not have a perfectly elliptical shape, e.g., electron trajectories may be influenced by fields which form the electron beam in a manner that no perfect elliptical shape of the beam is achieved or a start cross section may not allow to achieve a perfect elliptical shape, e.g., as the start cross section is not perfectly circular or elliptical.

[0022] The angular distribution of the electron beam depends on a position of the electron beam along the electron-optical axis and corresponds to the angles of electron trajectories relative to the electron-optical axis. The angular distribution includes an angle for each electron trajectory and may be represented by a maximal angle of the electron trajectory relative to the electron-optical axis. The maximal angle may be, for example, the angle of an electron trajectory of an electron beam disregarding outliers, such as, a maximal angle of only 99 % of the electron trajectories. The angular distribution in the energy dispersive direction at the proximal end may be represented by a maximal angle of the electron trajectory relative to the electron-optical axis in the energy dispersive direction at the proximal end. The angular distribution may alternatively be represented by statistics of angles included in the electron beam. As the electrons travelling through the electron imaging apparatus are subjected to electrostatic, magnetic, or electrostatic and magnetic fields, the electrontrajectories and their angles relative to the electron-optical axis are influenced by the forces caused by the fields. This changes the electron trajectories and angles of the electron trajectories relative to the electron-optical axis along the position in the direction of the electron-optical axis.

[0023] An electrostatic, magnetic or electrostatic and magnetic receiving field may be applied between the receiving aperture and the focal volume, e.g., a sample. This may change a cross section and angular distribution of the electron beam received at the receiving aperture from the start cross section at the surface of the focal volume and the start angles of the electrons of the electron beam relative to the electron-optical axis. The receiving field may allow to increase the number of electrons received at the receiving aperture.

[0024] The field generating unit may comprise one or more elements for generating one or more electrostatic, magnetic, or electrostatic and magnetic fields. For example, a circular beam shape of the electron beam may be transformed into an elliptical beam shape or sheet beam by a first field. As the number of electrons in the electron beam is limited in photoelectron spectroscopy, typically, there are no interactions between the electrons of an electron beam as their distance one after the other in the direction of the electron-optical axis is sufficiently large that their interactions can be neglected. Hence, a space charge effect of the electrons of the electron beams in photoelectron spectroscopy is negligible. Therefore, the first field may increase the angles in the angular distribution and thus lower the energy resolution. This negative effect may be mitigated by providing a second field with a distance between centers of the first field and the second field in the direction of the electron-optical axis, such that the angular distribution may be reduced again, e.g., to the start angular distribution or even below.

[0025] It is to be understood by the skilled person that not every desired shape of the cross section of the electron beam may be obtained when forming the electron beam as the achievable shape of the cross section of the electron beam depends on the start cross section and potentially further fields along the electron imaging apparatus. Preferably, the electron imaging apparatus transforms an electron beam with a circular shape to an elliptically shaped electron beam or sheet electron beam by changing the length of the elliptical axes. Also, the length of the elliptical axes of an initially elliptically shaped beam may be changed to transform the electron beam, e.g., reducing the height of the electron beam. This allows adjusting the height of the electron beam in the energy dispersive direction to a desired height in the energy dispersive direction at the proximal end.

[0026] Instead of a desired height of an electron beam in the energy dispersive direction at the proximal end, for example, a transmission probability or count rate of electrons through an aperture at the proximal end may be considered as the transmission probability and count rate depend on the desired height of the electron beam in the energy dispersive direction at the proximal end. In this case a desired transmission probability or desired count rate may be considered which may betransformed to a desired height of the electron beam in the energy dispersive direction at the proximal end that allows achieving the desired transmission probability or the desired count rate. Instead of an angular distribution of the electron beam in the energy dispersive direction at the proximal end, an energy resolution may be considered as the energy resolution depends on the angular distribution. In this case a desired energy resolution may be considered which may be transformed to a desired angular distribution in the energy dispersive direction at the proximal end which allows achieving the desired energy resolution. This equivalently applies for a combination of a desired transmission probability or desired count rate with a desired energy resolution. This allows achieving a desired energy resolution and desired count rate or desired transmission probability based on desired height of the electron beam and angular distribution in the energy dispersive direction at the proximal end.

[0027] The control unit may be part of the electron imaging apparatus or may be connected to the electron imaging apparatus. The control unit may be, for example, a computer with a processor, a memory and one or more interfaces, e.g., for connecting the control unit with the electron imaging apparatus and for receiving user inputs. The control unit may also comprise a power supply to provide control signals in form of voltage signals or be connected to a power supply to provide control signals to the power supply to cause the power supply to provide voltage signals.

[0028] The control unit may be configured for providing the at least one control signal to the field generating unit additionally based on at least one of the start cross section of the electron beam, start positions of the electrons, a cross section of the electron beam before entering the at least one electrostatic, magnetic, or electrostatic and magnetic field, an angular distribution of the electron beam before entering the at least one electrostatic, magnetic, or electrostatic and magnetic field, and the start angular distribution. The start position may be used to perform a spatially-resolved operating mode while the start angular distribution may be used to perform an angle-resolved operating mode. Alternatively, also an intensity operating mode may be performed.

[0029] Additionally, the control unit may be configured for providing the at least one control signal to the field generating unit based on any fields acting on the electron beam, e.g., a receiving field, accelerating fields, decelerating fields or any other field that may influence the cross section and / or angular distribution of the electron beam. This allows to account for the start conditions of the electron beam as well as any fields that influence the shape of the cross section of the electron beam as well as its angular distribution.

[0030] The at least one control signal may be configured for causing at least one power supply to provide at least one voltage signal with a respective voltage level to the field generating unit. For example, if the field generating unit comprises two quadrupoles with eight electrodes and an intermediate circumferential electrode, five different voltages may be provided, e.g., one voltagesignal for a pair of electrodes of the first quadrupole in the energy dispersive direction, one voltage signal for a pair of electrodes of the first quadrupole in a direction perpendicular to the energy dispersive direction, one voltage signal to the intermediate circumferential electrode, one voltage signal for a pair of electrodes of the second quadrupole in the energy dispersive direction, and one voltage signal for a pair of electrodes of the second quadrupole in the direction perpendicular to the energy dispersive direction. The respective voltage levels provided with the voltage signals may be optimized to allow generating fields to exert forces on the electrons of the electron beam such that the desired height of the electron beam in the energy dispersive direction is obtained at the proximal end and the desired angular distribution in the energy dispersive direction is obtained at the proximal end. The control unit may be configured for optimizing the respective voltage level of the at least one voltage signal based on calculations of the electron trajectories of the electron beam, for example, using initial voltage levels and iteratively adapting the voltage levels until the desired height and desired angular distribution in the energy dispersive direction is obtained at the proximal end. The electron trajectories may be determined using tools, e.g., computer simulation tools such as SIMION or COMSOL.

[0031] The field generating unit may comprise or be a beam forming lens. The field generating unit may be configured for forming the electron beam, e.g., from a circular to an elliptical shape or changing the elliptical axis lengths of an initially elliptically shaped beam. This allows transforming a circular beam into a sheet beam or elliptically shaped beam which better fits a rectangular aperture or entrance slit of an energy analyzer apparatus. In other words, the electron imaging apparatus allows changing a shape of the cross section of the electron beam and the angular distribution of the electron beam at an entrance to an analysis region so that the electron beam may better fit into the entrance aperture while controlling and preferably at least maintaining or reducing angular distribution in the energy dispersion plane.

[0032] The desired height may be selected to transfer a certain ratio of the electrons of the electron beam through an aperture, e.g., an exit slit of the electron imaging apparatus or an entrance slit of the energy analyzer apparatus. For example, the desired height may be selected to transfer above 50 %, e.g., above 60 %, or above 90 % of the electrons of the electron beam through the aperture. This allows to increase the count rate, transmission probability, or intensity by lowering a height of the electron beam in the energy dispersive direction, e.g., by reducing the elliptical axis length in the energy dispersive direction of the energy analyzer apparatus at the proximal end.

[0033] The desired angular distribution in the energy dispersive direction at the proximal end may be selected to achieve a desired energy resolution. Since the energy resolution depends on the angular distribution at the proximal end, e.g., corresponding to an entrance plane of the energy analyzer apparatus, and an entrance slit height of the energy analyzer apparatus, by selecting adesired angular distribution in the energy dispersive direction at the proximal end, the energy resolution may be adapted.

[0034] The field generating unit may be configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting a transverse force on the electrons in a direction perpendicular to the energy dispersive direction. Additionally, the field generating unit may be configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field has two perpendicular planes of symmetry and two planes of antisymmetry. The field generating unit may be configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting the transverse force on the electrons in the direction perpendicular to the energy dispersive direction to force the electrons further away from the electron-optical axis if the force exerted in the energy dispersive direction forces the electrons closer to the electron-optical axis and vice versa, i.e., such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting the transverse force on the electrons in the direction perpendicular to the energy dispersive direction to force the electrons closer to the electron-optical axis if the force exerted in the energy dispersive direction forces the electrons further away from the electron-optical axis. Preferably, the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting the transverse force on the electrons such that the electrons are forced further away from the electron-optical axis in the direction perpendicular to the energy dispersive direction and for exerting the force on the electrons such that the electrons are forced closer to the electron-optical axis in the energy dispersive direction. The angles of the electron trajectories are influenced by the transverse force and the force exerted on the electrons such that forcing the electrons further away from the electron-optical axis increases the angular distribution and forcing the electrons closer to the electron-optical axis reduces the angular distribution in the respective direction. If the angular distribution in the direction perpendicular to the energy dispersive direction is increased, the angular distribution in the energy dispersive direction is decreased. As the phase space volume of the electron beam, i.e., the product of the cross section, the angular distribution and the square root of a kinetic energy distribution of the electron beam, remains constant as the electron beam travels through the electron imaging apparatus without electrons getting removed from the electron beam, e.g., through hitting a surface of the electron imaging apparatus, an increase of the width of the electron beam or increase of the angular distribution in the direction perpendicular to the energy dispersive direction allowsdecreasing the angular distribution in the energy dispersive direction. A reduced angular distribution in the energy dispersive direction allows to achieve a higher energy resolution.

[0035] The field generating unit may be configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that a height of the electron beam at the proximal end of the electron imaging apparatus in the energy dispersive direction is reduced compared to a height of the electron beam at a distal end of the field generating unit or before entering the at least one electrostatic, magnetic, or electrostatic and magnetic field. This allows reducing the height of the electron beam by the field generating unit, e.g., such that the number of electrons passing through the aperture at the proximal end, e.g., the exit slit, may be increased by using the field generating unit.

[0036] The field generating unit may be configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the angular distribution in the energy dispersive direction at the proximal end is equal to or smaller than the start angular distribution in the energy dispersive direction. This allows to reduce the angular distribution in the energy dispersive direction at the proximal end such that the energy resolution may be improved compared to an electron beam with a higher angular distribution.

[0037] The field generating unit may be configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the angular distribution in the energy dispersive direction at the proximal end comprises angles relative to the electron-optical axis below 10°, preferably equal to or below 8°. This allows to provide an electron beam with electron trajectories that can be nearly parallel to each other. This allows to provide an optimal tradeoff between energy resolution and intensity or count rate.

[0038] The field generating unit may be configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the angular distribution in the energy dispersive direction at the proximal end is equal to or smaller than an angular distribution in the energy dispersive direction at the distal end of the field generating unit or before entering the at least one electrostatic, magnetic, or electrostatic and magnetic field. This allows maintaining or reducing the angular distribution of the electron beam by the field generating unit, e.g., such that the energy resolution can be maintained or improved, even when increasing the count rate of the electrons.

[0039] The field generating unit may be configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that an angle image of the focal volume, e.g., a sample, is provided in the direction perpendicular to the energy dispersive direction at the proximal end. This allows providing an angle image of the sample in a non-energy dispersive direction, e.g., a direction parallel to a longitudinal direction of anentrance slit of the energy analyzer apparatus.

[0040] Alternatively, the field generating unit may be configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that an image of the focal volume, e.g., a sample, is provided in the direction perpendicular to the energy dispersive direction at the proximal end. This allows providing an image of the sample in the direction perpendicular to the energy dispersive direction, e.g., non-energy dispersive direction, at an entrance slit of the energy analyzer apparatus.

[0041] The field generating unit may be configured for generating at least two electrostatic, magnetic, or electrostatic and magnetic fields arranged one after the other in the direction of the electron-optical axis. Providing a larger number of fields one after the other in the direction of the electron-optical axis increases the degrees of freedom for forming the shape of the cross section of the electron beam and manipulating the angular distribution of the electron beam. The at least two electrostatic, magnetic, or electrostatic and magnetic fields may be quadrupole fields, e.g., electrostatic quadrupole fields, magnetic quadrupole fields, or electrostatic quadrupole and magnetic quadrupole fields.

[0042] The field generating unit may comprise at least two sets of field generators configured for generating a multipole field such that forces act in the energy dispersive direction and perpendicular to the energy dispersive direction. This allows to provide even more degrees of freedom to form the shape of the electron beam and manipulate the angular distribution of the electron beam and to potentially correct for aberrations.

[0043] The field generating unit may comprise a first set of field generators and a second set of field generators. The first set and the second set may be arranged one after the other in the direction of the electron-optical axis with a distance to each other. Each of the sets of field generators may be configured for generating one of the at least two electrostatic, magnetic, or electrostatic and magnetic fields. In contrast to US 4,554,457 A, no poles made of a magnetic material need to be arranged at the ends of the magnetic lenses. This allows to avoid a reduction of the transmission of the lens and generation of scattering, which otherwise would reduce energy resolution of an electron spectrometer apparatus. Furthermore, costs may be reduced if, for example, two electrostatic quadrupoles are used, as magnetic lenses are large and expensive compared to an electrostatic quadrupole. Further technical problems such as temperature control and management and shielding from external magnetic fields while simultaneously localizing the magnetic field of the coil may be avoided or mitigated.

[0044] Each of the field generators may be configured for generating an electrostatic, a magnetic field or an electrostatic and magnetic field. Each set of field generators may comprise multiple field generators, preferably at least four field generators, arranged circumferentially aroundthe electron-optical axis, e.g., symmetrically arranged around the electron-optical axis to form a multipole, e.g., a quadrupole, for example a magnetic quadrupole or electrostatic quadrupole. The sets of field generators may be configured to act as stigmators or may be supplied with control signals such that they act as stigmators, e.g., quadrupole stigmators. The control unit may be configured to generate the at least one control signal, e.g., two control signals, to cause the sets of field generators to act as quadrupole stigmators such that each of the sets of field generators generates a quadrupole field for exerting a force on the electrons in the energy dispersive direction and a transverse force perpendicular to the energy dispersive direction. The control signal may be configured for providing a voltage to a pair of the field generators arranged in the energy dispersive direction and to a pair of the field generators arranged in the direction perpendicular to the energy dispersive direction of each set of the field generators such that an electrostatic or magnetic quadrupole field is generated by each of the sets which, for example, forces the electrons of the electron beams closer to the electron-optical axis in the energy dispersive direction and further away from the electron-optical axis in the direction perpendicular to the energy dispersive direction.

[0045] The field generators may have a length in the direction of the electron-optical axis of, for example, between 30 mm and 80 mm, e.g., between 40 mm and 60 mm. Two sets of field generators may have a distance in the direction of the electron-optical axis from each other of, for example, between one and two lengths of the field generators, e.g., between 30 mm and 160 mm, such as, between 40 mm and 120 mm. The distance between two sets of field generators may be fixed or variable, e.g., one or both of the sets may be moveable in the direction of the electron-optical axis. Using a fixed distance and geometry of the sets of field generators reduces costs while using a variable distance and / or geometry of the sets of field generators increases flexibility for creating fields and thus forming the electron beam and manipulating the angular distribution of the electron beam.

[0046] A distance between a respective center of the fields generated by each set of the field generators depends on the distance between the sets of the field generators. The distance between the respective centers of the fields may also depend on the control signal and may be adjusted in the direction of the electron-optical axis depending on, for example, voltage levels of voltage signals applied to each of the field generators as this may influence the form of the generated field and thus also the center of the field. The voltages to be applied to the field generators of the field generating unit to achieve a desired height of the electron beam in the energy dispersive direction at the proximal end and a desired angular distribution in the energy dispersive direction at the proximal end depend on the kinetic energy of the electrons when entering the at least one electrostatic, magnetic or electrostatic and magnetic field generated by the field generating unit. For example, in case of two quadrupoles arranged one after the other in the direction of the electron-optical axis,electrodes of the first quadrupole arranged in the energy dispersive direction may be supplied with a voltage level corresponding to 40 to 100 times the kinetic energy, electrodes of the first quadrupole arranged in the direction perpendicular to the energy dispersive direction may be supplied with a voltage level corresponding to 40 to 100 times the kinetic energy, electrodes of the second quadrupole arranged in the energy dispersive direction may be supplied with a voltage level corresponding to 10 to 40 times the kinetic energy, and electrodes of the second quadrupole arranged in the direction perpendicular to the energy dispersive direction may be supplied with a voltage level corresponding to 10 to 40 times the kinetic energy. A voltage signal may be applied to a circumferential electrode to form an intermediate potential between the two quadrupoles, e.g., with a voltage level between 0 and 20 times the kinetic energy. The voltage levels applied to the electrodes in the energy-dispersive direction and the direction perpendicular to the energy dispersive direction may be essentially the same, e.g., below 1 % deviation, or may deviate from each other, e.g., up to 20 times the kinetic energy. This allows generating a field adapted to the start conditions when entering the at least one electrostatic, magnetic, or electrostatic and magnetic field such that the electron beam may be formed and the angular distribution may be manipulated in a desired manner.

[0047] The field generating unit may comprise an electromagnetic solenoid with elliptical pole apertures at its distal end and at its proximal end. This may allow generating an electrostatic, magnetic, or electrostatic and magnetic field which may form the electron beam such that it has the desired height in the energy dispersive direction at the proximal end and the desired angular distribution in the energy dispersive direction at the proximal end. An electromagnetic solenoid with elliptical pole apertures at its distal end and its proximal end is known, for example, from S. Humphries et al. “Circular-to-planar transformations of high-perveance electron beams by asymmetric solenoid lenses”, published in Physical Review Special Topics - Accelerators and Beams, Volume 7, 060401 (2004), which is incorporated herein for reference. It is furthermore known from S. J. Russell et al. “First observation of elliptical sheet beam formation with an asymmetric solenoid lens”, published in Physical Review Special Topics - Accelerators and Beams, Volume 8, 080401 (2005), which is incorporated herein for reference, that an electromagnetic solenoid with elliptical pole apertures at its distal end and at its proximal end may show a similar performance than two quadrupoles arranged one after the other in the direction of the electron-optical axis.

[0048] The field generating unit may comprise at least one field generator with a non-cylindrical inner cross-section configured for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field such that a cross section of the electron beam is deformed to be significantly longer in the direction perpendicular to the energy dispersive direction than in theenergy dispersive direction. This allows forming an elliptically shaped electron beam using a single field generator. The cross section of the elliptically shaped electron beam may be compressed in the energy dispersive direction at the proximal end while the angular distribution is maintained or lowered in the energy dispersive direction at the proximal end.

[0049] The field generating unit may comprise a wire arrangement comprising at least one wire acting as an electrode. The wire arrangement may be configured and arranged for generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting the force on the electrons of the electron beam in the energy dispersive direction such that the height of the electron beam in the energy dispersive direction at the proximal end corresponds to the desired height in the energy dispersive direction at the proximal end and the angular distribution in the energy dispersive direction at the proximal end corresponds to the desired angular distribution in the energy dispersive direction at the proximal end. This allows compressing the cross section of the electron beam in the energy dispersive direction while maintaining or reducing the angular distribution in the energy dispersive direction at the proximal end.

[0050] The field generating unit may comprise a combination of electrostatic elements and magnetic elements. The electrostatic elements and the magnetic elements may be configured for correcting aberrations in the electron trajectories induced by the electron imaging apparatus. This allows providing aberration corrected images.

[0051] In a further aspect of the present invention an electron spectrometer apparatus is presented. The electron spectrometer apparatus comprises the electron imaging apparatus according to at least one of the claims 1 to 8 or any embodiment of the electron imaging apparatus, an energy analyzer apparatus, and a detector. The energy analyzer apparatus is configured for analyzing energies of electrons of an electron beam. The detector is configured for detecting the electrons of the electron beam. The electron imaging apparatus is configured for transferring electrons emitted from the focal volume, e.g. a sample, along the electron-optical axis of the electron imaging apparatus to the energy analyzer apparatus. This allows providing an improved electron spectrometer apparatus.

[0052] The electron spectrometer apparatus may comprise or be a photoelectron spectrometer, e.g., an angle resolved photoelectron spectrometer.

[0053] The detector may be a position sensitive detector, e.g., a multi-channeltron detector, multi-channel plate detector, a complementary metal -oxide-semiconductor (CMOS) detector, or delay line detector.

[0054] The electron spectrometer apparatus may comprise a sample holder configured for holding a sample.The energy analyzer apparatus may comprise a hemispherical energy analyzer. This allows increasing the count rate of a hemispherical electron spectrometer while maintaining energy and angular resolution or lateral resolution. The hemispherical energy analyzer may be an electrostatic deflector type particle energy analyzer.

[0055] In a further aspect of the present invention a material analysis system is presented. The material analysis system comprises an X-ray source, an X-ray monochromator, a vacuum chamber, and an electron spectrometer apparatus according to claim 9 or 10 or any embodiment of the electron spectrometer apparatus. The X-ray source is configured for providing X-rays. The X-ray monochromator is configured for generating monochromatic X-rays from the X-rays. The X-ray monochromator is configured and arranged to emit monochromatic X-rays to a focal volume in the vacuum chamber. The electron spectrometer apparatus is configured and arranged to receive and analyze electrons emitted by the focal volume in response to being hit by the monochromatic X-rays received from the X-ray monochromator. This allows providing an improved material analysis system. The material analysis system may for example be a photoelectron spectroscopy system for analyzing materials, layered structures, fluids, or devices and their properties.

[0056] The X-ray source may be configured for providing X-rays with different energies. The X-ray source may comprise an electron gun and anodes, each made of a different material. The electron gun may accelerate electrons on one of the anodes to generate X-rays. The anodes may for example be aluminum (Al), silver (Ag), titanium (Ti), chromium (Cr), copper (Cu), and gold (Au).

[0057] The X-ray monochromator may be configured to provide monochromatic X-rays with different energies, e.g., Al Ka with 1,49 keV, Ag La with 2,98 keV, Ag LB with 3,15 keV, Ti Ka with 4,51 keV, Cr Ka with 5,41 keV, Cu with 8,05 keV, and Au with 9,71 keV. The focal volume may be hit by X-rays of different energies such that, for example, different depths of a sample may be analyzed.

[0058] In a further aspect of the present invention a method for operating an electron imaging apparatus according to at least one of the claims 1 to 8 or any embodiment of the electron imaging apparatus is presented. The method comprises the steps:

[0059] generating by the control unit at least one control signal based on a desired height of the electron beam in an energy dispersive direction of the energy analyzer apparatus at the proximal end and a desired angular distribution in the energy dispersive direction at the proximal end,

[0060] providing the at least one control signal to the field generating unit, and

[0061] generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting a force on the electrons of the electron beam in the energy dispersive direction such that a height of the electron beam in the energydispersive direction at the proximal end corresponds to the desired height in the energy dispersive direction at the proximal end and an angular distribution in the energy dispersive direction at the proximal end corresponds to the desired angular distribution in the energy dispersive direction at the proximal end.

[0062] The method may comprise one or more of the steps:

[0063] generating by the control unit at least one control signal based on at least one of the start cross section of the electron beam, start positions of the electrons, a cross section of the electron beam before entering the at least one electrostatic, magnetic, or electrostatic and magnetic field, an angular distribution of the electron beam before entering the at least one electrostatic, magnetic, or electrostatic and magnetic field, and the start angular distribution,

[0064] generating by the field generating unit the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting a transverse force on the electrons in a direction perpendicular to the energy dispersive direction, and such that the at least one electrostatic, magnetic, or electrostatic and magnetic field has two perpendicular planes of symmetry and two planes of antisymmetry,

[0065] generating by the field generating unit the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the angular distribution in the energy dispersive direction at the proximal end is equal to or smaller than the start angular distribution in the energy dispersive direction,

[0066] generating by the field generating unit the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that an angle image of the focal volume is provided in the direction perpendicular to the energy dispersive direction at the proximal end,

[0067] generating by the field generating unit the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that an image of the focal volume is provided in the direction perpendicular to the energy dispersive direction at the proximal end,

[0068] generating by the field generating unit at least two electrostatic, magnetic, or electrostatic and magnetic fields arranged one after the other in the direction of the electron-optical axis,

[0069] generating by the field generating unit, the field generating unit comprising a first set of field generators and a second set of field generators arranged one after the other in the direction of the electron-optical axis with a distance to each other, each of the at least two electrostatic, magnetic, or electrostatic and magnetic fields by one of the sets of field generators,generating by an electromagnetic solenoid of the field generating unit, the electromagnetic solenoid comprising elliptical pole apertures at its distal end and at its proximal end, the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal,

[0070] generating by the field generating unit comprising a combination of electrostatic and magnetic elements the at least one electrostatic and magnetic field based on the at least one control signal.

[0071] In a further aspect of the present invention a use of the electron imaging apparatus, electron spectrometer apparatus, or the material analysis system is presented for: performing a surface analysis, measuring properties of a sample, measuring a surface reaction, measuring a fluid-solid-reaction, measuring a fluid-fluid-reaction, measuring a thin film, detecting a material in a fluid, performing a photoemission measurement, performing a photoelectron spectroscopy measurement, performing a near-ambient pressure measurement, performing a photoelectron spectroscopy measurement at near-ambient pressure, performing an electrochemical measurement, performing quality control, performing a measurement of a biological specimen, or performing a potentiometric measurement.

[0072] In a further aspect of the present invention a computer program product for operating an electron imaging apparatus according to at least one of the claims 1 to 8 or any embodiment of the electron imaging apparatus is presented. The computer program product comprises program code means for causing a processor to carry out the method according to claim 12 or 13, or any embodiment of the method, when the computer program product is run on the processor.

[0073] The control unit may comprise a processor configured for processing data, a computer readable medium in form of a memory, and an interface for communicating with the field generating unit.

[0074] The computer program product may alternatively or additionally be configured for operating the electron spectrometer apparatus according to claim 9 or 10 or any embodiment of the electron spectrometer apparatus or the material analysis system according to claim 11 or any embodiment of the material analysis system.

[0075] In a further aspect a computer readable medium having stored the computer program product of claim 14 is presented. Alternatively, or additionally, the computer readable medium can have the computer program product according to any embodiment of the computer program product stored.

[0076] It shall be understood that the electron imaging apparatus according to claim 1, the electron spectrometer apparatus according to claim 9, the material analysis system according to claim 11, the method according to claim 12, the computer program product of claim 14, and thecomputer readable medium of claim 15 have similar and / or identical preferred embodiments, in particular, as defined in the dependent claims.

[0077] It shall be understood that a preferred embodiment of the present invention can also be any combination of the dependent claims or above embodiments with the respective independent claim.

[0078] These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0079] BRIEF DESCRIPTION OF THE DRAWINGS

[0080] In the following drawings:

[0081] Fig. 1 shows schematically and exemplarily an embodiment of a material analysis system with an angle-resolved photoelectron spectrometer for analyzing material properties of a sample;

[0082] Fig. 2A shows schematically and exemplarily an embodiment of an energy analyzer apparatus connected to a position sensitive detector with electron trajectories with a maximal entrance angle to the energy analyzer apparatus of ap= 5°;

[0083] Fig. 2B shows schematically and exemplarily the embodiment of the energy analyzer apparatus connected to the position sensitive detector with electron trajectories with an entrance angle of ap= 0°;

[0084] Fig. 3 shows an embodiment of a magnetic quadrupole and the magnetic quadrupole field exerting forces on electrons;

[0085] Fig. 4 shows an embodiment of an electrostatic quadrupole and the electrostatic quadrupole field exerting forces on electrons;

[0086] Fig. 5 shows an embodiment of an electron imaging apparatus in which the control unit generates a control signal to form a cylindrically symmetric electron beam at a proximal end of the electron imaging apparatus;

[0087] Fig. 6 shows the cross section of the electron beam at the proximal end of the electron imaging apparatus of Fig. 5;

[0088] Fig. 7 shows the embodiment of the electron imaging apparatus in which the control unit generates a control signal to maximize transmission through an aperture at the proximal end of the electron imaging apparatus while angles of the electron trajectories relative to the electron-optical axis in an energy dispersive direction at the proximal end are less than 8° and a z-position of the electrons at the proximal end is proportional to a start angle of the electrons relative to the electron-optical axis in a direction perpendicular to the energy dispersive direction at the focal volume;Fig. 8 shows the cross section of the electron beam at the proximal end of the electron imaging apparatus of Fig. 7;

[0089] Fig. 9 shows the embodiment of the electron imaging apparatus in which the control unit generates a control signal to maximize transmission through the aperture at the proximal end of the electron imaging apparatus while the angle of the electron trajectories relative to the electron-optical axis in the energy dispersive direction at the proximal end are less than 8°;

[0090] Fig. 10 shows the cross section of the electron beam at the proximal end of the electron imaging apparatus of Fig. 9;

[0091] Fig. 11 shows the embodiment of the electron imaging apparatus in which the control unit generates a control signal to maximize transmission through the aperture at the proximal end of the electron imaging apparatus while the angles of the electron trajectories relative to the electron-optical axis in the energy dispersive direction at the proximal end are less than 8° and a z-position of the electrons at the proximal end is proportional to a start z-position at the focal volume;

[0092] Fig. 12 shows the cross section of the electron beam at the proximal end of the electron imaging apparatus of Fig. 11;

[0093] Fig. 13 shows a field generating unit in form of an electromagnetic solenoid with elliptical pole apertures at its distal end and at its proximal end;

[0094] Fig. 14 shows an embodiment of a method for operating an electron imaging apparatus to form an electron beam with a desired height in the energy dispersive direction and a desired angular distribution in the energy dispersive direction.

[0095] DETAILED DESCRIPTION OF EMBODIMENTS

[0096] Fig. 1 shows schematically and exemplarily an embodiment of a material analysis system 100 in form of a photoelectron spectroscopy system with an electron spectrometer apparatus 20 in form of an angle-resolved photoelectron spectrometer with a hemispherical energy analyzer for analyzing material properties of a sample 300. The material analysis system 100 can for example be used for performing a surface analysis, measuring properties of a sample, measuring a surface reaction, measuring a fluid-solid-reaction, measuring a fluid-fluid-reaction, measuring a thin film, detecting a material in a fluid, performing a photoemission measurement, performing a photoelectron spectroscopy measurement, performing a near-ambient pressure measurement, performing a photoelectron spectroscopy measurement at near-ambient pressure, performing an electrochemical measurement, performing quality control, performing a measurement of a biological specimen, or performing a potentiometric measurement.

[0097] The material analysis system 100 comprises an X-ray source 12, an X-ray monochromator 14, the electron spectrometer apparatus 20, a vacuum pump 30, and a vacuumchamber 40. In this embodiment, the X-ray source 12, X-ray monochromator 14 and electron spectrometer apparatus 20 are arranged in the vacuum chamber 40. In other embodiments, for example, only the sample 300 or the sample 300 and parts of the electron spectrometer apparatus 20 may be arranged in the vacuum chamber 40.

[0098] The X-ray source 12 generates X-rays of different wavelengths. In this embodiment an electron gun fires electrons on different anode materials to generate the X-rays of different wavelengths. The X-ray monochromator 14 generates monochromatic X-rays X from the X-rays received from the X-ray source 12. The X-ray monochromator 14 comprises reflecting mirrors adapted to focus and monochromatize the X-rays of specific wavelengths, e.g., having between 1 keV and 10 keV, such as Al Ka with 1,49 keV, Ag La with 2,98 keV, Ag LB with 3,15 keV, Ti Ka with 4,51 keV, Cr Ka with 5,41 keV, Cu with 8,05 keV, and Au with 9,71 keV. The X-ray monochromator 14 emits and focuses monochromatic X-rays X to a focal volume 200 in the vacuum chamber 40. In this embodiment the focal volume 200 is part to the surface of the sample 300 with a spot size of 10 pm. In other embodiments, the spot size may also be different, e.g., between 1 pm and 400 pm, preferably between 10 pm and 100 pm. The focal volume 200 emits electrons e in response to being hit by the monochromatic X-rays X received from the X-ray monochromator 14. The electrons e are received in the electron spectrometer apparatus 20. The electron spectrometer apparatus 20 analyzes the electrons e.

[0099] The electron spectrometer apparatus 20 is an angle resolved photoelectron spectrometer in this embodiment and comprises an electron imaging apparatus 23, an energy analyzer apparatus 26, and a detector 28. The electron spectrometer apparatus 20 may optionally include a sample holder (not shown) for holding the sample 300. The sample holder may also be a separate unit. The sample holder may be moveable and tiltable to scan the sample 300. Additionally, the sample 300 may be scanned by scanning over the anode material with the electron gun of the X-ray source 12 (not shown). This also allows adjusting a position of the focal volume 200 with respect to the sample 300.

[0100] The electron imaging apparatus 23 transfers the electrons e emitted from the focal volume 200 of the sample 300 along an electron-optical axis 500 extending along a center axis of the electron imaging apparatus 23 from its distal end 80 to its proximal end 90 (cf. Figs. 5, 7, 9, 11) which is connected to the energy analyzer apparatus 26 (cf. Figs. 2A and 2B). The electron imaging apparatus 23 is used to form a shape of the electron beam 25 and manipulate an angular distribution of the electron beam 25. In more detail, the electron imaging apparatus 23 is used to adapt a height of the electron beam or a height of its cross section, respectively, to a desired height dH in an energy dispersive direction y at the proximal end 90 of the electron imaging apparatus 23 (cf. Figs.

[0101] 6, 8, 10, 12) and to adapt an angular distribution in the energy dispersive direction y to a desiredangular distribution with a maximal angle apin the energy dispersive direction y at the proximal end 90 (cf. Figs. 5, 7, 9, 11). The electron imaging apparatus 23 is described in more detail with respect to Figs. 5, 7, 9, and 11 in the following. Same reference signs correspond to essentially identical components.

[0102] The electron imaging apparatus 23 has a receiving aperture 22, electron lens groups 24, a field generating unit 65, and a control unit 400.

[0103] The receiving aperture 22 is arranged at the distal end 80 of the electron imaging apparatus 23 and receives the electrons e from the focal volume 200 emitting electrons e from multiple start positions with multiple start angles a in the energy dispersive direction y and Az in the non-energy dispersive direction z relative to the electron-optical axis 500. The electrons e received by the receiving aperture 22 form the electron beam 25 with a start cross section at a surface of the focal volume 200 of the sample 300 and a start angular distribution based on the start angles a and Az of the electrons e received by the receiving aperture 22.

[0104] In the embodiments of the electron imaging apparatus 23 shown in Figs. 5, 7, 9, and 11, the field generating unit 65 generates two electrostatic fields 61 (cf. Fig. 4) arranged one after the other in the direction x of the electron-optical axis 500. The field generating unit 65 comprises a first set 60 of field generators in form of electrodes 62, 64, 66, 68 and a second set 60’ of field generators in form of electrodes 62’, 64’, 66’, 68’. The first set 60 and the second set 60’ are arranged one after the other in the direction x of the electron-optical axis 500 with a distance to each other and each of the sets 60 and 60’ of the field generators 62, 64, 66, 68, 62’, 64’, 66’, 68’ generates one of the two electrostatic fields 61. In this embodiment, the field generating unit 65 has two quadrupoles 60, 60’ operated as quadrupole stigmators. The electrostatic field 61 and its generation is described in more detail with regard to Fig. 4.

[0105] Instead of two electrostatic fields, one ore more electrostatic, magnetic or electrostatic and magnetic fields may be generated. For example, in another embodiment, the field generating unit may be or may comprise an electromagnetic solenoid with elliptical pole apertures at its proximal and distal ends (cf. Fig. 13). The field generating unit may, alternatively, comprise two or more electrostatic multipoles or a combination of electrostatic and magnetic multipoles. The multipoles preferably have at least 4 electrostatic or magnetic elements that are, e.g., concentrically arranged around the electron-optical axis with pairs of elements arranged on opposite sides of the electron-optical axis.

[0106] The control unit 400 comprises a processor 410, a computer readable medium 420 in form of a memory, a user interface 430, and an interface 440. The control unit 400 is part of the electron imaging apparatus 23. In other embodiments, the control unit may alternatively be connected to the electron imaging apparatus 23 and form part of the material analysis system 100 orpart of the electron spectrometer apparatus 20.

[0107] The control unit 400 in this embodiment controls the operation of the electron imaging apparatus 23. In other embodiments, the control unit 400 may also be configured for controlling the material analysis system 100 and its components or the electron spectrometer apparatus 20 and its components.

[0108] The control unit 400 provides at least one control signal to the field generating unit 65 based on the desired height dH of the electron beam 25 in the energy dispersive direction y of the energy analyzer apparatus 23 at the proximal end 90 and the desired angular distribution apin the energy dispersive direction y at the proximal end 90.

[0109] The processor 410 is configured for processing data and for generating control signals. The control signals may be, for example, voltage signals with certain voltage levels supplied to the pairs of field generators of the sets 60 and 60’ of the field generators 62, 64, 66, 68, 62’, 64’, 66’, and 68’ or may also be signals to control a power supply such that the power supply provides the voltage signals with certain voltage levels to the pairs of field generators of the sets 60 and 60’ of the field generators. The voltage signals may be determined, for example, based on iteratively determining and optimizing electron trajectory simulations for various voltage signals, e.g., using a tool such as SIMION or COMSOL. The voltage signals may be varied until, for example, a difference between the desired target value, e.g., the desired height and desired angular distribution, to the simulated values is sufficiently small or until a certain number of iteration steps was performed.

[0110] The computer readable medium 420 stores a computer program product which comprises program code means for causing the processor 410 to carry out a method for operating the electron imaging apparatus 23, e.g., the method 1400 shown in Fig. 14 or any embodiment of that method, when the computer program product is run on the processor 410.

[0111] The user interface 430 receives inputs from the user and provides outputs to a user. The inputs of the user may be, for example, the desired height and the desired angular distribution in the energy dispersive direction y at the proximal end 90 of the electron imaging apparatus 23 or an input related to these parameters, e.g., a desired count rate or desired intensity and a desired energy resolution.

[0112] The interface 440 is used to connect the field generating unit 65 with the control unit 400. The interface 400 may comprise, for example, cables or lines for providing the voltage signals. In other embodiments, the interface 440 may connect further components of the material analysis system 100 with the control unit 400.

[0113] The field generating unit 65 generates the two electrostatic fields 61 based on the control signals such that the two electrostatic fields 61 exert a force F2 and F4 on the electrons e ofthe electron beam 25 in the energy dispersive direction y and a transverse force Fi and F3 in the direction z perpendicular to the energy dispersive direction y such that a height of the electron beam 25 in the energy dispersive direction y at the proximal end 90 corresponds to the desired height dH in the energy dispersive direction y at the proximal end 90 and the angular distribution in the energy dispersive direction y at the proximal end 90 corresponds to the desired angular distribution apin the energy dispersive direction y at the proximal end 90.

[0114] In other embodiments, the field generating unit may be configured for generating at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting a force on the electrons of the electron beam in the energy dispersive direction such that a height of the electron beam in the energy dispersive direction at the proximal end corresponds to the desired height in the energy dispersive direction at the proximal end and an angular distribution in the energy dispersive direction at the proximal end corresponds to the desired angular distribution in the energy dispersive direction at the proximal end.

[0115] Since the field generating unit 65 comprises two quadrupoles operating as stigmators for generating electrostatic quadrupole fields perpendicular to the electron beam 25 the cross section of the electron beam can be compressed in the energy dispersive direction y of the energy analyzer apparatus 26 at the proximal end 90 of the electron imaging apparatus 23 and the angular distribution of the electron beam 25 can be maintained or reduced in the energy dispersive direction y at the proximal end 90 of the electron imaging apparatus 23 compared to the start angular distribution or an angular distribution at a distal end of the field generating unit 65 or an angular distribution before entering the at least one electrostatic quadrupole field.

[0116] The electron beam 25 thus formed is provided to the energy analyzer apparatus 26 through an aperture. In this embodiment an exit slit of the electron imaging apparatus 23 and an entrance slit 72 of the energy analyzer apparatus 26 have identical dimensions. In other embodiments, the electron imaging apparatus and the energy analyzer apparatus may share the same slit as exit slit of the electron imaging apparatus and entrance slit of the energy analyzer apparatus.

[0117] In this embodiment, the energy analyzer apparatus 26 is a hemispherical energy analyzer which analyzes energies of electrons e of the electron beam 25 as shown in Figs. 2A and 2B.

[0118] In this embodiment, the detector 28 is a position sensitive detector in form of a channel detector which detects the electrons e of the electron beam 25 which were analyzed in and passed the energy analyzer apparatus 26.

[0119] The vacuum pump 30 generates an ultra high vacuum in the vacuum chamber 40. Inother embodiments, further pumps may be present, e.g., for generating different levels of vacuum at different parts of the electron imaging apparatus 23 to perform near ambient pressure X-ray photoelectron spectroscopy (not shown).

[0120] The electron spectrometer apparatus 20 of the material analysis system 100 may be operated, for example, in an angle-resolved operating mode, a spatially-resolved operating mode, or an intensity operating mode. The intensity is typically reduced if the electron spectrometer apparatus 20 is operated in the angle-resolved operating mode or spatially-resolved operating mode. For performing the angle-resolved operating mode, the start angular distribution or the respective start angles of the electrons e of the electron beam 25 are important (cf. Fig 6 and 8). For performing the spatially-resolved operating mode, the start positions of the electrons e of the electron beam 25 are important (cf. Fig. 12). For an intensity operating mode, the start position and start angular distribution are not important (cf. Fig. 10).

[0121] Figs. 2A and 2B show an embodiment of an energy analyzer apparatus 26 in form of a hemispherical energy analyzer with electron trajectories of electrons e of an electron beam 25 received from an energy imaging apparatus 23 (cf. Fig. 1). The electrons e enter the energy analyzer apparatus 26 through an entrance slit 72 with height H in an energy dispersive direction y, corresponding to the direction along a radius of the hemisphere, at three different start positions (red, green and black trajectories in colour drawings; gray, light gray, and black trajectories in grayscale drawings). In this embodiment the height H of the entrance slit in energy dispersive direction y is 7 mm and a width in a direction z perpendicular to the entrance slit 72 is 30 mm (not shown). In other embodiments, the height of the entrance slit 72 in the energy dispersive direction y may be, for example, between 1 mm and 10 mm, and the width in the direction z perpendicular to the energy dispersive direction y may be, for example, between 10 mm and 40 mm. An angular distribution of the electron beam 25 in the energy dispersive direction y has a maximal entrance angle apof an electron e relative to the electron-optical axis 500 into the entrance slit 72 of ap= 5° in Fig. 2A and ap= 0° in Fig. 2B. The electrons e of the electron beam 25 are separated according to their kinetic energy E at detector plane 74 before hitting a detector 28 in form of a position sensitive detector. In this embodiment the detector is a channel detector. In other embodiments the detector may also be another type of detector, e.g., multi-channeltron detector, a multi-channel plate detector, a CMOS detector, or a delay line detector. The kinetic energy of the electrons increases in direction E at the detector plane 74. Typically kinetic energies around an average kinetic energy + / -10 % have to be separated. The electrons which have kinetic entrance energy or pass energy Ep, an entrance angle of 0° and which pass through the center of the entrance slit 72 corresponding to the electron-optical axis 500 have an electron trajectory along radius Roof the energy analyzer apparatus 26 (center black trajectory in Fig 2B).To achieve maximal intensity or count rate with the electron spectrometer apparatus 20 and hence reduce measurement time, the electron imaging apparatus 23 should transfer as much of the electrons e emitted by the focal volume 200 through the entrance slit 72 of the energy analyzer apparatus 26 as possible. In other words, an acceptance area and acceptance angle for the focal volume 200 of the sample 300 should be as large as possible.

[0122] The energy resolution AE of the energy analyzer apparatus 26 in form of the hemispherical energy analyzer is influenced by its extension or height in the energy dispersive direction y, as well as by the maximal entrance angle apof the electron trajectories of the electron beam 25. The height of the electron beam 25 in the energy dispersive direction y is typically limited by a height H of the entrance slit 72 of the energy analyzer apparatus 26. If the height of the electron beam 25 is larger than the height H of the entrance slit 72, some of the electrons e of the electron beam 25 cannot enter the energy analyzer apparatus 26 and hit a wall such that the count rate is reduced. The energy resolution AE becomes worse if the height of the electron beam 25 in the energy dispersive direction y in the energy analyzer apparatus 26 or the maximal entrance angle apof the electron trajectories of the electron beam 25 increase as the energy resolution AE of the

[0123]

[0124] To achieve a high count rate and good energy resolution, the height of the electron beam 25 in the energy dispersive direction y should be optimized to be small enough to fit into the entrance slit 72 with height H such that a high number of electrons enter the energy analyzer apparatus 26 and do not hit a wall before entering the energy analyzer apparatus 26. Furthermore, the angular distribution apof the electron beam 25 in the energy dispersive direction y at the entrance slit 72 should be small. The electron beam 25 thus needs to be formed to fit into the entrance slit 72 and the angular distribution apneeds to be manipulated such that the maximal entrance angle apis small, e.g., below 10°, such as 8° or lower. The electron beam 25 can be formed and the angular distribution can be manipulated by at least one electrostatic, magnetic, or electrostatic and magnetic field. Increasing the degrees of freedom for manipulating the field allows to improve the forming of the electron beam and manipulating of the angular distribution.

[0125] Preferably, the electron imaging apparatus comprises a field generating unit with two quadrupoles arranged one after the other in the direction of the electron-optical axis or another field generating unit which can generate a single field which allows simultaneous forming of the electron beam and manipulating the angular distribution such that the electron beam fits into the slit while the angular distribution is kept small, e.g., using an electromagnetic solenoid with elliptical apertures at its distal end and proximal end.

[0126] Fig. 3 shows schematically and exemplary a cross section of an embodiment of afield generating unit in form of a magnetic quadrupole 50 with two pairs of identical magnets arranged circumferentially around an electron-optical axis 500. Magnets 52 and 56 are arranged to have a south pole and magnets 54 and 58 are arranged to have a north pole such that forces F2 and F4 generated by the magnetic field 51 in an energy dispersive direction y force the electron e closer to the electron-optical axis 500 and such that forces Fi and F3 generated by the magnetic field 51 in a direction z perpendicular to the energy dispersive direction y force the electron e further away from the electron-optical axis 500. The magnetic quadrupole 50 may be used to form an electron beam, e.g., from a circular to an elliptical shape.

[0127] The magnetic quadrupole 50 thus generates the magnetic field 51 based on a control signal such that the magnetic field 51 exerts a transverse force Fi and F3 on the electrons e in the direction z perpendicular to the energy dispersive direction y and such that the magnetic field 51 has two perpendicular planes of symmetry and two planes of antisymmetry.

[0128] Fig. 4 shows schematically and exemplary a cross section of another embodiment of a field generating unit in form of an electrostatic quadrupole 60 with four electrodes arranged symmetrically around an electron-optical axis 500. Electrodes 62 and 66 are supplied with a negative voltage and electrodes 64 and 68 are supplied with a positive voltage such that forces F2 and F4 generated by the electrostatic field 61 in an energy dispersive direction y force the electron e closer to the electron-optical axis 500 and such that transverse forces Fi and F3 generated by the electrostatic field 61 in a direction z perpendicular to the energy dispersive direction y force the electron e further away from the electron-optical axis 500. The electrostatic quadrupole 60 may be used to form an electron beam, e.g., from a circular to an elliptical shape. In this embodiment the lengths of the electrodes 62 to 68 in the direction x of the electron-optical axis x is 50 mm and identical for each of the electrodes 62 to 68. In other embodiments, the lengths in the direction of the electron-optical axis may also be, for example, between 40 mm and 100 mm.

[0129] The electrostatic quadrupole 60 thus generates the electrostatic field 61 based on a control signal such that the electrostatic field 61 exerts a transverse force Fi and F3 on the electrons e in the direction z perpendicular to the energy dispersive direction y and such that the electrostatic field 61 has two perpendicular planes of symmetry and two planes of antisymmetry.

[0130] In other embodiments, the field generating unit may also be configured for generating the at least one electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic and magnetic field is configured for exerting a transverse force on the electrons in a direction perpendicular to the energy dispersive direction, and such that the at least one electrostatic and magnetic field has two perpendicular planes of symmetry and two planes of antisymmetry. In another embodiment, for example, a combination of the two quadrupoles of electrodes and magnets shown in Figs. 3 and 4 may be arranged circumferentially around theelectron-optical axis (not shown).

[0131] Fig. 5 shows an embodiment of an electron imaging apparatus 23 in which the control unit 400 generates a control signal to form a cylindrically symmetric electron beam 23 at a proximal end 90 of the electron imaging apparatus 23. Electron trajectories are shown in the energy dispersive plane x-y on the left side and in the plane x-z perpendicular to the energy dispersive plane x-y, i.e., the non-energy dispersive plane x-z, on the right side. The electron trajectories of the electrons emitted by the focal volume 200 start at the focal volume 200 of the sample 300 with a start angle a relative to the electron-optical axis 500 in the energy dispersive direction y which vary between -30° and 30° with an interval of 5° and with a start azimuth angle Az relative to the electron-optical axis 500 in the non-energy dispersive direction z between -30° and 30° with an interval of 5°. The electrons enter the electron imaging apparatus 23 through its receiving aperture 22 at its distal end 80 and form an electron beam 25. The electron beam 25 is transferred along the electron-optical axis 500 from the distal end 80 to the proximal end 90, which is connected to the energy analyzer apparatus 26 (cf. Figs.

[0132] 2 A and 2B).

[0133] Only the field generating unit 65 and its function is explained in detail while other electrode components or electron lens components, e.g., meshes, of the electron lens group 24 along the electron-optical axis 500 are only schematically shown but no further details are provided. The electron lens group 24 may influence and manipulate the electron beam, e.g., focus and / or deflect the electron beam or generate a Gaussian or parallel image at a certain position. The skilled person understands that the electron beam may be transferred along the electron imaging apparatus 23 in various ways, for example, using various types of lens groups, e.g., various electron lens components and an electron deflector as disclosed in EP 3712924 Bl.

[0134] The field generating unit 65 comprises the first set 60 of field generators in form of electrodes 62, 64, 66, 68 and the second set 60’ of field generators in form of electrodes 62’, 64’, 66’, 68’ as described above. In other embodiments, the field generating unit 65 may have additional components, e.g., further electrodes, e.g., for forming an intermediate potential between the two sets 60 and 60’ or an entrance electrode at the entrance to the field generating unit 65 or an exit electrode at an exit of the field generating unit 65.

[0135] In this embodiment, the voltage signals applied to the sets 60 and 60’ generate a cylindrically symmetrical electron beam 25 with radial positions of the electrons at the proximal end 90 being proportional to the start azimuth angle Az at the focal volume 200. In this embodiment, the start positions of the electrons, e.g., an electron distribution, is simulated as a point source at the focal volume 200 with a single kinetic energy.

[0136] Part of the electron trajectories of the electron beam 25 end at the proximal end 90 in the energy dispersive direction y at a wall of an exit slit, which has identical dimensions and is directlyconnected to an entrance slit 72 of the energy analyzer apparatus 26. Hence, an angular distribution with a maximal entrance angle apenter the energy analyzer apparatus 26. In this embodiment apis 8°. In other embodiments apis preferably below 10° to have a decent energy resolution.

[0137] The extension of the electron beam 25 in the direction z perpendicular to the energy dispersive direction y, i.e., in the non-energy dispersive direction z, and the angular distribution in the non-energy dispersive direction z have only a low influence on the energy resolution of the electron spectrometer apparatus 20. Using a position sensitive imaging detector allows to analyze information in the non-energy dispersive direction z. When operating the electron imaging apparatus 23 of the electron spectrometer apparatus 20 in an angle-resolved operating mode the distance of the energy dispersive plane x-y at the detector 28 is proportional to the start azimuth angle in the non-energy dispersive direction z. When operating the electron imaging apparatus 23 of the electron spectrometer apparatus 20 in a spatially-resolved operating mode the distance of the energy dispersive plane x-y at the detector 28 is proportional to the start position of the electrons in the non-energy dispersive direction z.

[0138] Fig. 6 shows the cross section of the electron beam 25 at the proximal end 90 of the electron imaging apparatus 23 of Fig. 5 corresponding to the cross section at the entrance slit 72 of the energy analyzer apparatus 26. The electron imaging apparatus 23 in Fig. 5 and 6 is operated in an angle-resolved operating mode. The Z coordinate corresponds to the start azimuth angles Az in the x-z plane. The entrance slit 72 has a height H of 7 mm and a width of 30 mm. Only electrons e of the electron beam 25 within the entrance slit 72 are transferred to the energy analyzer apparatus 26. The electrons e outside of the entrance slit 72 hit a wall and are absorbed. In Fig. 6, only 33% of the electrons e are transferred which means that the transmission through the entrance slit 72 is 33%. This reduces the count rate of the electron spectrometer apparatus 20.

[0139] Fig. 7 shows the embodiment of the electron imaging apparatus 23 in which the control unit 400 generates a control signal to maximize transmission through an aperture at the proximal end 90 of the electron imaging apparatus 23 while an angle of the electrons relative to the electron-optical axis 500 in an energy dispersive direction y at the proximal end 90 is less than 8° and a z-position of the electrons at the proximal end 90 is proportional to a start Azimuth angle, i.e., an angle of the electrons relative to the electron-optical axis 500 in a direction z perpendicular to the energy dispersive direction y at the focal volume 200. Fig. 7 shows the same electron imaging apparatus 23 as Fig. 5 in a different operation, namely to increase transmission. Identical reference signs describe identical components or units of the electron imaging apparatus 23. The electron imaging apparatus 23 in Fig. 7 and 8 is operated in an angle-resolved operating mode. The electron trajectories of the electrons emitted by the focal volume 200 start at the focal volume 200 of the sample 300 with a start angle a relative to the electron-optical axis 500 in the energy dispersivedirection y which vary between -30° and 30° with an interval of 1° and with a start azimuth angle Az relative to the electron-optical axis 500 in the non-energy dispersive direction z between -30° and 30° with an interval of 5°. As the angular distribution apin the energy dispersive direction y at the proximal end 90 is less than 8°, it is thus smaller than the start angular distribution a which include electrons with maximal angles of -30° to 30° relative to the electron-optical axis 500.

[0140] In Fig. 7, the field generating unit hence generates the two electrostatic fields based on the control signals such that the angular distribution apin the energy dispersive direction y at the proximal end 90 is smaller than the start angular distribution a in the energy dispersive direction y and such that an angle image of the focal volume 200 of the sample 300 is provided in the direction z perpendicular to the energy dispersive direction y at the proximal end 90.

[0141] Fig. 8 shows the cross section of the electron beam 25 at the proximal end 90 of the electron imaging apparatus 23 of Fig. 7 corresponding to the cross section at the entrance slit 72 of the energy analyzer apparatus 26. The electron imaging apparatus 23 in Fig. 7 and 8 is operated in an angle-resolved operating mode. The Z coordinate corresponds to the start azimuth angles Az in the x-z plane. The entrance slit 72 has a height H of 7 mm and a width of 30 mm. In Fig. 8, the transmission through the entrance slit 72 is 92 %.

[0142] Fig. 9 shows the embodiment of the electron imaging apparatus 23 in which the control unit 400 generates a control signal to maximize transmission through the aperture at the proximal end 90 of the electron imaging apparatus 23 while an angle of the electrons e relative to the electron-optical axis 500 in the energy dispersive direction y at the proximal end 90 is less than 8°. Fig. 9 shows the same electron imaging apparatus 23 as Fig. 7 in a different operating mode, namely an intensity operating mode. Identical reference signs describe identical components or units of the electron imaging apparatus 23. The electron trajectories of the electrons emitted by the focal volume 200 start at the focal volume 200 of the sample 300 with a start angle a relative to the electron-optical axis 500 in the energy dispersive direction y which vary between -30° and 30° with an interval of 1° and with a start azimuth angle Az relative to the electron-optical axis 500 in the non-energy dispersive direction z between -30° and 30° with an interval of 1°.

[0143] Fig. 10 shows the cross section of the electron beam 25 at the proximal end 90 of the electron imaging apparatus 23 of Fig. 9 corresponding to the cross section at the entrance slit 72 of the energy analyzer apparatus 26. The electron imaging apparatus 23 in Fig. 9 and 10 is operated in an intensity operating mode. A start angular distribution at the focal volume 200 of the sample 300 is a cone with half angle of 30°. The entrance slit 72 has a height H of 7 mm and a width of 30 mm. In Fig. 10, the transmission through the entrance slit 72 is 94 %.

[0144] Fig. 11 shows the embodiment of the electron imaging apparatus 23 in which the control unit 400 generates a control signal to maximize transmission through the aperture at theproximal end 90 of the electron imaging apparatus 23 while an angle of the electrons e relative to the electron-optical axis 500 in an energy dispersive direction y at the proximal end 90 is less than 8° and a z-position of the electrons e at the proximal end 90 is proportional to a start z-position Zstart at the focal volume 200 of the sample 300. Fig. 11 shows a similar electron imaging apparatus 23 as Fig. 5, 7 and 9. The electron imaging apparatus 23 has a different number of electrodes and electron lens components of the electron lens group 24 before the electron beam 25 enters the field generating unit 65. This difference is not described in detail and other embodiments with different electron lens groups for transferring the electron beam 25 between the distal end 80 and a distal end of the field generating unit 65 are known to the skilled person. Furthermore, the electron imaging apparatus 23 of Fig. 11 is operated in a spatially-resolved operating mode.

[0145] Identical reference signs describe identical components or units of the electron imaging apparatus 23. The electron trajectories of the electrons e emitted by the focal volume 200 start at the focal volume 200 of the sample 300 with a start angle a relative to the electron-optical axis 500 in the energy dispersive direction y which vary between -1° and 1° with an interval of 0.33° and start z-and y-positions of the electrons e vary between -1 and 1 mm with an interval of 0.25 mm in the z-direction and 0.2 mm in the y-direction, respectively. The electron trajectories have a single kinetic energy.

[0146] The field generating unit 65 of the electron imaging apparatus 23 generates the two electrostatic fields based on the control signals such that an image of the focal volume 200 of the sample 300 is provided in the direction z perpendicular to the energy dispersive direction y at the proximal end 90.

[0147] Fig. 12 shows the cross section of the electron beam 25 at the proximal end of the electron imaging apparatus of Fig. 11. Fig. 11 shows the spatially-resolved operating mode of the electron spectrometer apparatus 20. The cross-section of the electron beam 25 completely fits in the rectangular entrance slit 72 of the energy analyzer apparatus 26, i.e., the desired height dH of the electron beam 25 in the energy dispersive direction y at the proximal end of the electron imaging apparatus is smaller than the height H of the entrance slit 72 and the width of the electron beam in the direction z perpendicular to the energy dispersive direction y is smaller than the width of the entrance slit 72 such that the transmission through this aperture is 100%. The entrance slit 72 has a height of 7 mm and a width of 20 mm in this embodiment. The Z coordinates of the electron trajectories of the electron beam 25 correspond to start positions Zstart in the direction z perpendicular to the energy dispersive direction y.

[0148] Fig. 13 shows a field generating unit 1300 in form of an electromagnetic solenoid 1302 with elliptical pole apertures 1304 at its distal end 1380 and at its proximal end 1390. The field generating unit 1300 may be included in an electron imaging apparatus to generate a field forforming an electron beam and manipulating the angular distribution of the electron beam. Fig. 14 shows an embodiment of a method 1400 for operating an electron imaging apparatus, e.g., the electron imaging apparatus 23 shown in Fig. 1, 5, 7, 9, or 11, to form an electron beam 25 with a desired height dH in the energy dispersive direction y and a desired angular distribution with a maximal entrance angle of apin the energy dispersive direction y.

[0149] In step 1402 a user enters a desired height of the electron beam in the energy dispersive direction of the energy analyzer apparatus at the proximal end corresponding to the height of the electron beam at an entrance slit to the energy analyzer apparatus and a desired angular distribution in the energy dispersive direction at the proximal end. Step 1402 is optional. Instead of entering the desired height and desired angular distribution, for example, a desired count rate or intensity and energy resolution may be entered. The method may be adapted to transform these into desired height and desired angular distribution to achieve them. Alternatively, one or both of the desired height and desired angular distribution may be predetermined, e.g., the angular distribution may have a maximal entrance angle of 10° or below, such as 8° or less.

[0150] In step 1404, the control unit generates at least one control signal based on the desired height of the electron beam in the energy dispersive direction of the energy analyzer apparatus at the proximal end and the desired angular distribution in the energy dispersive direction at the proximal end. The control signal depends on the number of field generators included in the field generating unit. In case of two sets of quadrupoles with two pairs of electrodes, a total of four voltage signals with four voltage levels may be generated as control signals to the pairs of electrodes to control the fields generated by the quadrupoles. In other embodiments, the control signal may additionally be generated based on one or more of a start cross section of the electron beam, start positions of the electrons, a cross section of the electron beam before entering the at least one electrostatic, magnetic, or electrostatic and magnetic field, an angular distribution of the electron beam before entering the at least one electrostatic, magnetic, or electrostatic and magnetic field, and the start angular distribution at the focal volume.

[0151] In step 1406, the at least one control signal is provided from the control unit to the field generating unit. In case of the two sets of quadrupoles, the voltages are supplied to the respective pairs of electrodes.

[0152] In step 1408, the field generating unit, e.g., the two sets of quadrupoles, generate the at least one electrostatic, magnetic, or electrostatic and magnetic field, e.g., two electrostatic fields, based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field exerts a force on the electrons of the electron beam in the energy dispersive direction such that a height of the electron beam in the energy dispersive direction at the proximal end corresponds to the desired height in the energy dispersive direction at the proximalend and an angular distribution in the energy dispersive direction at the proximal end corresponds to the desired angular distribution in the energy dispersive direction at the proximal end. The field generating unit, e.g., the two sets of quadrupoles, may in step 1408 additionally generate the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field exerts a transverse force on the electrons in a direction perpendicular to the energy dispersive direction, and such that the at least one electrostatic, magnetic, or electrostatic and magnetic field has two perpendicular planes of symmetry and two planes of antisymmetry,

[0153] This allows providing a formed electron beam with a desired height in the energy dispersive direction at the proximal end and a desired angular distribution in the energy dispersive direction at the proximal end to an energy analyzer apparatus. The electrons of the electron beam can be analyzed and detected in further steps to perform, for example, photoelectron spectroscopy. Different operating modes of an angle resolved photoelectron spectrometer, such as an angle-resolved operating mode, a spatially-resolved operating mode or an intensity operating mode may be used to derive different properties from the focal volume of the sample. For example, an image or an angle image of the focal volume may be provided in the direction perpendicular to the energy dispersive direction at the proximal end. An aberration correction may be performed, e.g., by using a combination of electrostatic and magnetic elements for generating the at least one electrostatic and magnetic field based on the at least one control signal.

[0154] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

[0155] For the processes and methods disclosed herein, the operations performed in the processes and methods may be implemented in differing order. Furthermore, the outlined operations are only provided as examples, and some of the operations may be optional, combined into fewer steps and operations, supplemented with further operations, or expanded into additional operations without detracting from the essence of the disclosed embodiments.

[0156] In the claims, the word "comprising", “including”, or “containing” does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality.

[0157] A single unit or device may fulfil the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0158] Procedures like generating by the control unit at least one control signal, providing the at least one control signal to the field generating unit, generating the at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal, etc. can beperformed by any other number of modules, units, or devices. These procedures can be implemented as program code means of a computer program and / or as dedicated hardware.

[0159] A computer program product may be stored / distributed on a suitable medium, such as an optical storage medium or a solid-state medium, supplied together with or as part of other hardware, but may also be distributed in other forms, such as via the Internet or other wired or wireless telecommunication systems.

[0160] Any modules or units described herein may be processing units that are part of a classical computing system. Processing units may include a general-purpose processor and may also include a field programmable gate array (FPGA), an application-specific integrated circuit (ASIC), or any other specialized circuit. Any memory may be a physical system memory, which may be volatile, non-volatile, or some combination of the two. The term “memory” may include any computer-readable storage media such as a non-volatile mass storage. If the computing system is distributed, the processing and / or memory capability may be distributed as well. The computing system may include multiple structures as “executable components”. The term “executable component” is a structure well understood in the field of computing as being a structure that can be software, hardware, or a combination thereof. For instance, when implemented in software, one of ordinary skill in the art would understand that the structure of an executable component may include software objects, routines, methods, modules, and so forth, that may be executed on the computing system. This may include both an executable component in the heap of a computing system, or on computer-readable storage media. The structure of the executable component may exist on a computer-readable medium such that, when interpreted by one or more processors of a computing system, e.g., by a processor thread, the computing system is caused to perform a function. Such structure may be computer readable directly by the processors, for instance, as is the case if the executable component were binary, or it may be structured to be interpretable and / or compiled, for instance, whether in a single stage or in multiple stages, so as to generate such binary that is directly interpretable by the processors. In other instances, structures may be hard coded or hard wired logic gates, that are implemented exclusively or near-exclusively in hardware, such as within a FPGA, an ASIC, or any other specialized circuit. Accordingly, the term “executable component” is a term for a structure that is well understood by those of ordinary skill in the art of computing, whether implemented in software, hardware, or a combination. Any embodiments herein are described with reference to acts that are performed by one or more processing units of the computing system. If such acts are implemented in software, one or more processors direct the operation of the computing system in response to having executed computer-executable instructions that constitute an executable component. Computing system may also contain communication channels that allow the computing system to communicate with other computing systems over, forexample, network. A “network” is defined as one or more data links that enable the transport of electronic data between computing systems and / or modules and / or other electronic devices. When information is transferred or provided over a network or another communications connection, for example, either hardwired, wireless, or a combination of hardwired or wireless, to a computing system, the computing system properly views the connection as a transmission medium.

[0161] Transmission media can include a network and / or data links which can be used to carry desired program code means in the form of computer-executable instructions or data structures and which can be accessed by a general-purpose or special-purpose computing system or combinations. While not all computing systems require a user interface, in some embodiments, the computing system includes a user interface system for use in interfacing with a user. User interfaces act as input or output mechanism to users for instance via displays.

[0162] Those skilled in the art will appreciate that at least parts of the invention may be practiced in network computing environments with many types of computing system configurations, including, personal computers, desktop computers, laptop computers, message processors, hand-held devices, multi-processor systems, microprocessor-based or programmable consumer electronics, network PCs, minicomputers, main-frame computers, mobile telephones, PDAs, pagers, routers, switches, datacenters, wearables, such as glasses, and the like. The invention may also be practiced in distributed system environments where local and remote computing system, which are linked, for example, either by hardwired data links, wireless data links, or by a combination of hardwired and wireless data links, through a network, both perform tasks. In a distributed system environment, program modules may be located in both local and remote memory storage devices.

[0163] Those skilled in the art will also appreciate that at least parts of the invention may be practiced in a cloud computing environment. Cloud computing environments may be distributed, although this is not required. When distributed, cloud computing environments may be distributed internationally within an organization and / or have components possessed across multiple organizations. In this description and the following claims, “cloud computing” is defined as a model for enabling on-demand network access to a shared pool of configurable computing resources, e.g., networks, servers, storage, applications, and services. The definition of “cloud computing” is not limited to any of the other numerous advantages that can be obtained from such a model when deployed. The computing systems of the figures include various components or functional blocks that may implement the various embodiments disclosed herein as explained. The various components or functional blocks may be implemented on a local computing system or may be implemented on a distributed computing system that includes elements resident in the cloud or that implement aspects of cloud computing. The various components or functional blocks may beimplemented as software, hardware, or a combination of software and hardware. The computing systems shown in the figures may include more or less than the components illustrated in the figures and some of the components may be combined as circumstances warrant.

[0164] Any reference signs in the claims should not be construed as limiting the scope. The present invention relates to an electron imaging apparatus configured to be connected to an energy analyzer apparatus. The electron imaging apparatus comprises a receiving aperture, a control unit, and a field generating unit. The receiving aperture is configured for receiving electrons from a focal volume which form an electron beam. The control unit is configured for providing a control signal to the field generating unit based on a desired height of the electron beam in an energy dispersive direction of the energy analyzer apparatus at a proximal end of the electron imaging apparatus and a desired angular distribution in the energy dispersive direction at the proximal end. The field generating unit is configured for generating at least one electrostatic, magnetic, or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic, magnetic, or electrostatic and magnetic field is configured for exerting a force on the electrons of the electron beam in the energy dispersive direction such that a height of the electron beam in the energy dispersive direction at the proximal end corresponds to the desired height in the energy dispersive direction at the proximal end and an angular distribution in the energy dispersive direction at the proximal end corresponds to the desired angular distribution in the energy dispersive direction at the proximal end.

Claims

CLAIMS:

1. An electron imaging apparatus (23) configured for transferring an electron beam (25) along an electron-optical axis (500) extending along a center axis of the electron imaging apparatus (23) from its distal end (80) to its proximal end (90), the proximal end (90) being configured to be connected to an energy analyzer apparatus (26), wherein the electron imaging apparatus (23) comprises:a receiving aperture (22) at the distal end (80) configured for receiving electrons (e) from a focal volume (200) emitting electrons (e) from multiple start positions with multiple start angles (a, Az) relative to the electron-optical axis (500), wherein the electrons (e) received by the receiving aperture (22) form an electron beam (25) with a start cross section at a surface of the focal volume (200), and a start angular distribution based on the start angles (a, Az) of the electrons (e) received by the receiving aperture (22),a field generating unit (65; 1300) configured for generating at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field, anda control unit (400) configured for providing at least one control signal to the field generating unit (65; 1300) based on a desired height (dH) of the electron beam (25) in an energy dispersive direction (y) of the energy analyzer apparatus (26) at the proximal end (90) and a desired angular distribution< in the energy dispersive direction (y) at the proximal end (90),wherein the field generating unit (65; 1300) is configured for generating the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field is configured for exerting a force (F2, F4) on the electrons (e) of the electron beam (25) in the energy dispersive direction (y) such that a height of the electron beam (25) in the energy dispersive direction (y) at the proximal end (90) corresponds to the desired height (dH) in the energy dispersive direction (y) at the proximal end (90) and an angular distribution in the energy dispersive direction (y) at the proximal end (90) corresponds to the desired angular distribution< in the energy dispersive direction (y) at the proximal end (90).

2. The electron imaging apparatus (23) according to claim 1, wherein the field generating unit (65; 1300) is configured for generating the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field is configured for exerting a transverse force (Fi, F3) on the electrons (e) in a direction (z) perpendicular to the energy dispersive35direction (y), and such that the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field has two perpendicular planes of symmetry and two planes of antisymmetry.

3. The electron imaging apparatus (23) according to claim 1 or 2, wherein the field generating unit (65; 1300) is configured for generating the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal such that the angular distribution < in the energy dispersive direction (y) at the proximal end (90) is equal to or smaller than the start angular distribution in the energy dispersive direction (y).

4. The electron imaging apparatus (23) according to at least one of the claims 1 to 3, wherein the field generating unit (65; 1300) is configured for generating the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal such that an angle image of the focal volume (200) is provided in a direction (z) perpendicular to the energy dispersive direction (y) at the proximal end (90).

5. The electron imaging apparatus (23) according to at least one of the claims 1 to 3, wherein the field generating unit (65; 1300) is configured for generating the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal such that an image of the focal volume (200) is provided in a direction (z) perpendicular to the energy dispersive direction (y) at the proximal end (90).

6. The electron imaging apparatus (23) according to at least one of the claims 1 to 5, wherein the field generating unit (65) is configured for generating at least two electrostatic (61), magnetic (51), or electrostatic and magnetic fields arranged one after the other in the direction (x) of the electron-optical axis (500).

7. The electron imaging apparatus (23) according to claim 6, wherein the field generating unit (65) comprises a first set (60) of field generators (62, 64, 66, 68) and a second set (60’) of field generators (62’, 64’, 66’, 68’), wherein the first set (60) and the second set (60’) are arranged one after the other in the direction (x) of the electron-optical axis (500) with a distance to each other, and wherein each of the sets (60, 60’) of field generators (62, 64, 66, 68, 62’, 64’, 66’, 68’) is configured for generating one of the at least two electrostatic (61), magnetic (51), or electrostatic and magnetic fields.

8. The electron imaging apparatus (23) according to at least one of the claims 1 to 7,36wherein the field generating unit (1300) comprises an electromagnetic solenoid (1302) with elliptical pole apertures (1304) at its distal end (1380) and at its proximal end (1390).

9. An electron spectrometer apparatus (20) comprising:the electron imaging apparatus (23) according to at least one of the claims 1 to 8, an energy analyzer apparatus (26) configured for analyzing energies (E) of electrons (e) of an electron beam (25), anda detector (28) for detecting the electrons (e) of the electron beam (25),wherein the electron imaging apparatus (23) is configured for transferring electrons (e) emitted from the focal volume (200) along the electron-optical axis (500) of the electron imaging apparatus (23) to the energy analyzer apparatus (26).

10. The electron spectrometer apparatus (20) according to claim 9, wherein the energy analyzer apparatus (26) comprises a hemispherical energy analyzer (26).

11. Material analysis system (100) comprisingan X-ray source (12) configured for providing X-rays,an X-ray monochromator (14) configured for generating monochromatic X-rays (X) from the X-rays,a vacuum chamber (40), andan electron spectrometer apparatus (20) according to claim 9 or 10,wherein the X-ray monochromator (14) is configured and arranged to emit monochromatic X-rays (X) to a focal volume (200) in the vacuum chamber (40) andwherein the electron spectrometer apparatus (20) is configured and arranged to receive and analyze electrons (e) emitted by the focal volume (200) in response to being hit by the monochromatic X-rays (X) received from the X-ray monochromator (14).

12. A method (1400) for operating an electron imaging apparatus (23) according to at least one of the claims 1 to 8 comprising the steps:generating by the control unit (400) at least one control signal based on a desired height (dH) of the electron beam (25) in an energy dispersive direction (y) of the energy analyzer apparatus (26) at the proximal end (90) and a desired angular distribution< in the energy dispersive direction (y) at the proximal end (90),providing the at least one control signal to the field generating unit (65; 1300), and generating the at least one electrostatic (61), magnetic (51), or electrostatic andmagnetic field based on the at least one control signal such that the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field is configured for exerting a force (F2, F4) on the electrons (e) of the electron beam (25) in the energy dispersive direction (y) such that a height of the electron beam (25) in the energy dispersive direction (y) at the proximal end (90) corresponds to the desired height (dH) in the energy dispersive direction (y) at the proximal end (90) and an angular distribution in the energy dispersive direction (y) at the proximal end (90) corresponds to the desired angular distribution< in the energy dispersive direction (y) at the proximal end (90).

13. The method (1400) according to claim 12 comprising one or more of the steps:generating by the control unit (400) at least one control signal based on at least one of the start cross section of the electron beam (25), start positions of the electrons (e), a cross section of the electron beam (25) before entering the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field, an angular distribution of the electron beam (25) before entering the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field, and the start angular distribution,generating by the field generating unit (65; 1300) the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal such that the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field is configured for exerting a transverse force (Fi, F3) on the electrons (e) in a direction (z) perpendicular to the energy dispersive direction (y), and such that the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field has two perpendicular planes of symmetry and two planes of antisymmetry,generating by the field generating unit (65; 1300) the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal such that the angular distribution< in the energy dispersive direction (y) at the proximal end (90) is equal to or smaller than the start angular distribution in the energy dispersive direction (y),generating by the field generating unit (65; 1300) the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal such that an angle image of the focal volume (200) is provided in the direction (z) perpendicular to the energy dispersive direction (y) at the proximal end (90),generating by the field generating unit (65; 1300) the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal such that an image of the focal volume (200) is provided in the direction (z) perpendicular to the energy dispersive direction at the proximal end (90),generating by the field generating unit (65) at least two electrostatic (61), magnetic (51),or electrostatic and magnetic fields arranged one after the other in the direction (x) of the electron-optical axis (500),generating by the field generating unit (65; 1300), the field generating unit (65; 1300) comprising a first set (60) of field generators (62, 64, 66, 68) and a second set (60’) of field generators (62’, 64’, 66’, 68’) arranged one after the other in the direction (x) of the electron-optical axis (500) with a distance to each other, each of the at least two electrostatic (61), magnetic (51), or electrostatic and magnetic fields by one of the sets (60, 60’) of field generators (62, 64, 66, 68, 62’, 64’, 66’, 68’),generating by an electromagnetic solenoid (1302) of the field generating unit (1300), the electromagnetic solenoid (1302) comprising elliptical pole apertures (1304) at its distal end (1380) and at its proximal end (1390), the at least one electrostatic (61), magnetic (51), or electrostatic and magnetic field based on the at least one control signal, andgenerating by the field generating unit (65) comprising a combination of electrostatic and magnetic elements the at least one electrostatic and magnetic field based on the at least one control signal.

14. Computer program product for operating an electron imaging apparatus (23) according to at least one of the claims 1 to 8, wherein the computer program product comprises program code means for causing a processor (410) to carry out the method as defined in claim 12 or 13, when the computer program product is run on the processor (410).

15. Computer readable medium (420) having stored the computer program product of claim 14.39

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